rust-by-practice/en/src/variables.md

Variables

Binding and mutablity

1. 🌟 A variable can be used only if it has been initialized.

// fix the error below with least modifying
fn main() {
    let x: i32; // uninitialized but using, ERROR !
    let y: i32; // uninitialized but also unusing, only warning

    assert_eq!(x, 5);
    println!("Success!")
}

2. 🌟 Use mut to mark a variable as mutable.

// fill the blanks in code to make it compile
fn main() {
    let __ =  1;
    __ += 2; 
    
    assert_eq!(x, 3);
    println!("Success!")
}

Scope

A scope is the range within the program for which the item is valid.

3. 🌟

// fix the error below with least modifying
fn main() {
    let x: i32 = 10;
    {
        let y: i32 = 5;
        println!("The value of x is {} and value of y is {}", x, y);
    }
    println!("The value of x is {} and value of y is {}", x, y); 
}

4. 🌟🌟

// fix the error with using of define_x
fn main() {
    println!("{}, world", x); 
}

fn define_x() {
    let x = "hello";
}

Shadowing

You can declare a new variable with the same name as a previous variable, here we can say **the first one is shadowed by the second one.

5. 🌟🌟

// only modify `assert_eq!` to make the `println!` work(print `42` in terminal)
fn main() {
    let x: i32 = 5;
    {
        let x = 12;
        assert_eq!(x, 5);
    }

    assert_eq!(x, 12);

    let x =  42;
    println!("{}", x); // Prints "42".
}

6. 🌟🌟

// remove a line in code to make it compile
fn main() {
    let mut x: i32 = 1;
    x = 7;
    // shadowing and re-binding
    let x = x; 
    x += 3;


    let y = 4;
    // shadowing
    let y = "I can also be bound to text!"; 

    println!("Success!")
}

Unused varibles

1. fix the warning below with :

• 🌟 only one solution
• 🌟🌟 two distinct solutions

Note: none of the solutions is to remove the line let x = 1

fn main() {
    let x = 1; 
}

// warning: unused variable: `x`

Destructuring

8. 🌟🌟 We can use a pattern with let to destructure a tuple to separate variables.

Tips: you can use Shadowing or Mutability

// fix the error below with least modifying
fn main() {
    let (x, y) = (1, 2);
    x += 2;

    assert_eq!(x, 3);
    assert_eq!(y, 2);

    println!("Success!")
}

Destructuring assignments

Introducing in Rust 1.59: You can now use tuple, slice, and struct patterns as the left-hand side of an assignment.

9. 🌟🌟

Note: the feature Destructuring assignments need 1.59 or higher Rust version

fn main() {
    let (x, y);
    (x,..) = (3, 4);
    [.., y] = [1, 2];
    // fill the blank to make the code work
    assert_eq!([x,y], __);

    println!("Success!")
} 

You can find the solutions here(under the solutions path), but only use it when you need it